Production of asymmetric porous film materials
AssigneeSumitomo Electric Industries, Ltd.
InventorKoichi Okita
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Abstract
Porous film materials composed of polytetrafluoroethylene having an asymmetric structure are produced by stretching the film using a pair of revolving rolls which are heated to a temperature lower than the melting point of the film. Stretching is produced by revolving the two rolls at different speeds which also tends to produce a compressive force in the thickness of the film. The rolls are heated to different temperatures to produce a temperature difference of preferably 50.degree. C. or more. The combination of the compressive force and the temperature gradient in the thickness of the film is believed to produce the asymmetric structure in the resulting porous film materials which are characterized by a fiber structure in the surface which is different from that in the back.
Claims4
A process for producing asymmetric porous film materials which comprises
- molding a polytetrafluoroethylene containing a liquid lubricating agent by a paste method to form a film,
- removing the liquid lubricating agent, and
- generating a temperature difference simultaneously with a compressive force in the thickness direction of the film during stretching the film at a temperature lower than the sintering temperature of the polytetrafluoroethylene using rolls
- which have a different revolving ratio and
- which have a temperature difference between each other,
- whereby tension is caused by the stretching direction of the film while a compressive force corresponding to the tension is caused in the thickness direction of the film.
Dependencies are inferred from the claim text.